1. Field of the Invention
The present invention relates generally to a method and apparatus for transmitting a control channel in a mobile communication system and a system thereof. In particular, the present invention relates to a method and apparatus for transmitting a Data Rate Control (DRC) channel by a mobile station (MS) to control a rate of forward packet data received from a base station (BS) in a High Rate Packet Data (HRPD) system, and a system thereof.
2. Description of the Related Art
With the increase in the use of packet data service based on wireless networks, research is being conducted on high-speed data transmission in a Code Division Multiple Access (CDMA) mobile communication system. A 1x Evolution Data Only (1xEV-DO) system is an example of such a typical high rate packet data system having a channel structure for the high-speed data transmission. The 1xEV-DO system was proposed by the 3rd Generation Partnership Project 2 (3GPP2), a standardization group for synchronous mobile communication technology, to make up for the defects of data communication supported by the IS-200 system.
A structure of forward channels in the 1xEV-DO system will now be described. A pilot channel, a Medium Access Control (MAC) channel, a forward traffic channel, and a forward control channel, are transmitted by time division multiplexing (TDM). A group of the TDM-transmitted signals is typically called a ‘burst’. The forward traffic channel transmits user data packets, and the forward control channel transmits control messages and user data packets. The forward MAC channel is used to transmit reverse rate control and power control information or transmit a designation channel for forward data transmission.
Reverse channels of the 1xEV-DO system, unlike the forward channels, include channels having a unique identification code for each individual terminal. The reverse channels for each individual terminal include a pilot channel, a reverse traffic channel, an access channel, a DRC channel, and a Reverse Rate Indicator (RRI) channel. The reverse traffic channel transmits user data packets, the DRC channel is used to indicate a forward rate supportable by a terminal, and the RRI channel is used to indicate a rate of a data channel transmitted in the reverse direction. The access channel is used when the terminal transmits messages or traffic to the base station before the traffic channel is connected.
With reference to FIG. 1, a description will now be made of an exemplary configuration and rate control operation of the 1xEV-DO system, and channels related thereto.
Referring to FIG. 1, the 1xEV-DO system performs data transmission/reception between access terminals (At) or mobile stations (MS) 10a, 10b and 10c shown at 10 and a packet network, via a Packet Data Service Node (PDSN) 40. The PDSN 40 is connected to the packet network such as the Internet 50, and an Access Network (AN) or base stations (BS). The AN or BS can include Access Network Transceiver Systems (ANTS) or base station transceiver systems (BTS) 20a and 20b shown at 20, and Access Network Controllers (ANC) or base station controllers (BSC) 30a and 30b shown at 30. The AN wirelessly communicates with a plurality of ATs 10, and transmits the high-rate packet data to an AT having the highest rate.
The 1xEV-DO system is an example of a high rate packet data system to which embodiments of the present invention can be applied. The AT corresponds to the MS, and the AN corresponds to the BS. In the following description, the general terms “MS” and “BS” will be used for the AT and AN, respectively.
In the 1xEV-DO system of FIG. 1, for rate control for a forward channel, the MS 10 measures reception strength of a pilot channel signal transmitted by the BS 20 and determines a forward data rate at which the corresponding MS 10 can receive the signal, based on the measured reception strength of the pilot channel signal. The MS 10 transmits DRC information for the determined forward data rate to the BS 20 over a DRC channel. Then, the BS 20 receiving the DRC information can transmit packet data only to the MS 10 having the best channel condition at the rate reported by the corresponding MS 10. Although a mapping relation between the forward channel condition and the DRC information can differ according to system implementation, it is generally fixed in an MS manufacturing process.
FIG. 2 is a diagram illustrating an exemplary operation in which an MS transmits the unit DRC information according to a DRCLength indicated by a BS. That is, the MS repeatedly transmits DRC information for the forward channel every DRC length (DRCLength) indicated by the BS.
In this context, in a first exemplary case of a DRCLength=1, the MS determines a DRC value and transmits the determined DRC value over a DRC channel every slot, and the BS receives the DRC information and uses the received DRC information as information on a rate at which the corresponding MS desires to receive data at one corresponding slot in the forward traffic channel. In a second exemplary case of a DRCLength=2, the MS determines a DRC value and transmits the determined DRC value over a DRC channel every two slots, and the BS receives the DRC information and uses the received DRC information as information on a rate at which the corresponding MS desires to receive data for the two corresponding slots in the forward traffic channel.
Similarly, in an exemplary case of a DRCLength=4, 8, . . ., the MS determines a DRC value and transmits the determined DRC value to the BS every slot corresponding to the DRCLength, and the BS uses the received DRC information as information on a rate at which the corresponding MS desires to receive data for the slots corresponding to the DRCLength in the forward traffic channel. Although the MS can transmit the unit DRC information for a longer time at lower transmission power as the DRCLength is longer as described with reference to FIG. 2, the use of the method described with reference to FIG. 2 cannot rapidly take the channel conditions into account because of the increase in the time required for transmitting the unit DRC information.
The conventional DRC channel transmission technology was proposed to control a rate of one forward traffic channel through one DRC channel. However, for future high-speed data systems using a plurality of Frequency Allocations (FAs), i.e., in which one MS uses a plurality of forward traffic channels, like the 3x system, there is a need for a DRC channel transmission scheme that is capable of efficiently controlling rates of a plurality of forward traffic channels.